Sen. Ted Cruz (R-TX) is the latest GOP presidential contender to unveil a detailed tax plan. His proposal, outlined in a Wall Street Journal op-ed (asistraditional), is legitimately shocking — it will cost trillions upon trillions of dollars and lead to an enormous tax cut for the richest Americans.

Here are the basics:

A 10 percent flat tax on all individual income, whether from wages or investment

A 10 percent flat tax is the lowest rate proposed by any candidate to date. Rand Paul, the only other candidate with a detailed flat tax plan, wants a 14.5 percent rate — and even that is estimated to lose $1.8 trillion according to the right-leaning Tax Foundation, or $15 trillion, according to the left-leaning Citizens for Tax Justice. Ben Carson has in the past gestured at a 10 percent rate, inspired by biblical tithing, but he has since said on Marketplace and in the CNBC debate that the real rate would be closer to 15 percent. Cruz truly stands alone here.

Currently, the top 0.1 percent of households, which make an average of $9.4 million a year, have an average effective federal individual income tax rate of 26.5 percent. Cruz would cut that to under 10 percent. It’s a truly massive tax cut for the richest Americans.

Cruz also stands apart for calling for the complete elimination of payroll taxes. It’s an astonishingly costly proposal, which would leave funding for Social Security and Medicare in jeopardy.

Cruz would replace one of the most progressive taxes with a regressive one

Cruz isn’t unique in his support for a VAT. Paul would also replace the corporate tax with a VAT, a policy that both Cruz and Paul have weirdly borrowed from California Gov. Jerry Brown’s 1992 Democratic primary bid. But this is a much more radical corporate tax proposal than any candidate but Bobby Jindal (who wants to eliminate corporate taxes altogether) is proposing.

It’s also a regressive proposal. While corporate taxes are among the most progressive taxes the federal government levies, VATs are regressive by nature. Jim Nunns of the Tax Policy Center has found that about 20 percent is paid by workers, and the rest by capital. He concludes that in 2015 the top 1 percent pays 52.8 percent of the corporate tax burden, and the top 0.1 percent pays 33.4 percent.

But because VATs are a kind of consumption tax, they fall mostly on the poor. In 2010, the poorest 20 percent of Americans spent 163.2 percent of their income, largely by going into lots of debt. The richest top 0.1 percent, by contrast, only spent 9.1 percent of their income. So when the Tax Policy Center evaluated a plan for a 12.9 percent VAT, they found that the lowest quintile would pay 10.9 percent of their income, on average — and the top 0.1 percent would only pay 6.7 percent. Abandoning a corporate tax for a VAT would mean giving up a massively progressive tax for a quite regressive one. That might not increase inequality if the VAT were used to fund progressive programs, which is how they’re used in European social democracies. But I doubt Cruz wants that.

Cruz’s plan makes some sense from a supply-sider standpoint — but not as much as you’d think

The weirdest part of Cruz’s plan is that it doesn’t do the sorts of things the most radical GOP plans usually do to try to boost investment and economic growth. He taxes investment income, while traditional flat tax plans have never done that — and his rival Marco Rubio would eliminate taxes on investment altogether. Ten percent would be a lot lower than the 23.8 percent top rate on capital gains income, so he’d be reducing taxes on investment substantially (and, from a supply-side standpoint, boosting investment), but he would eliminate any preference for that income.

He would add a $25,000 investment deduction, which wouldn’t mean much for the richest investors and also would be ineffective at spurring more savings among poorer Americans. For example, a big study found that in Denmark, providing $1 in tax incentives to save only increased savings by $0.01 — one measly cent. Even if you think that decreasing taxes on savings would, on the margin, promote investment, this is a very strange way to do it. Even progressives who support consumption taxes, like Robert Frank, generally want investment deductions like this to be unlimited.